1. Field of the Invention
The present invention relates to lenitives, primers and fillers used for odontotherapies and, more particularly, to lenitives for hypersensitivity, coating primers and root canal filling materials.
2. Prior Art
Among stimuli to teeth are hypersensitivity and pulpalgia that are clincally considered to offer grave problems.
Hypersensitivity is induced, as when vital teeth are put in a senso-sthenic condition by exposure of their dentines and come into physical or chemical contact with cold or sweet-sour foods and drinks, chill, galvanic current, toothbrushes, toothpicks, etc., and causes induced pain and acute pain, although they are transient or fugitive.
The Braom's hydrodynamic theory about the mechanism of hypersensitivity teaches that an external stimulus applied to the surface of dentine causes a tissue (or pulpal) fluid to move through dentinal tubules in an inward or outward direction and thereby stimulates dentinal nerves in the pulp to cause pain.
As various other theories have also been suggested about the mechanism of hypersensitivity, however, it has so far been treated by such various therapies as set out below.
(1) Mechanical protection of the surface of exposed dental tubules against stimuli of external origin. To this end, a paraformaldehyde-containing "Hyperband" is coated on those surfaces.
(2) Protection of dental tubules against stimuli of external origin by promoting their intra-calcification for their closure. To this end, a "Saforide" containing a diammine silver fluoride solution or an "F vanish" containing a sodium fluoride is coated on the dental tubules --therapy (2-1). Alternatively, the principle of iontophoresis is applied to feed a drug ionized in a solution deeply into the affected region with the aid of current--Therapy (2-2).
(3) A silver nitrate solution is coated on odontoblasts to modify and coagulate them, thereby keeping them from reacting with stimuli of external origin.
(4) Irradiation of laser beams.
These therapies (1)-(4) have been found to be inefficacious for those who suffer from hypersensitivity, i.e. these have the following defects.
For instance, the coating of the paraformaldehyde containing "Hyperband" so as to protect the surfaces of exposed dentinal tubules mechanically against stimuli of external origin--therapy (1)--involves much work, since the powder and liquid components must be mixed and kneaded together for use, and is thus restricted by time, because a period as long as 5-6 hours is needed to set the powder/liquid mixture completely. Moreover, the efficacy of Therapy (1) is generally as low as 50%.
Therapy (2-1), in which the "Saforide" containing a diammine silver fluoride or the F vanish containing a sodium fluoride is applied on dentinal tubules to promote their intra-calcification to close up them and thereby protect them against stimuli of external origin, blackens the affected region coated, and is thus not desirable from the aesthetic point of view and unfit for adults. Moreover, the efficacy of therapy (2-1) is generally as low as 47%. Problems with therapy (2-2) or iontophoresis therapy, in which the principles of electrophoresis is applied to feed a drug ionized in a solution deeply into the affected part with the aid of a current, are that an expensive ion feeder is needed; it involves much work; it causes the patient to feel fright; and the like. Moreover, therapy (2-2) does not pay off for operation, as understood from its efficacy being generally as low as 40%.
Therapy (3), in which odontoblasts are modified and coagulated by the coating of a silver nitrate solution to keep them from reacting with stimuli of external origin, makes the region coated blackish brown, and is thus aesthetically not desirable and unfit for adults. Moreover, it generally shows an efficacy of at most 50%.
Therapy (4) by the irradiation of laser beams, in which laser beams are applied to the dentinal surface of the affected part for about 1 minute, is efficacious, but needs a costly laser irradiator. Moreover, therapy (4) shows an 80% efficacy in some cases, but it is not good in others.
The therapies so far used to treat hypersensitivity do not only involve time-consuming and troublesome work but also may need special equipment. Even without it, they incurs considerable expense. From the patients' point of view, on the other hand, one problem is that the region coated becomes black and so aesthetically not desirable. Another problem is that for lack of durable effect, the affected region has to be coated periodically. Thus, clinicians have yet to find crucially efficacious therapy in spite of many people suffering from hypersensitivity.
Pulpalgia, on the other hand, is induced by physical or chemical factors such as cavity preparation, tooth preparation for fixed prosthodontics, resin filling, traumatic occlusion, changes in atmospheric pressure, fatigue and food debris, and causes every pain from acute, pulsating and lancinating pains to slight pains. Pulpalgia by and large is considered to be causes for similar reasons to those mentioned about hypersensitivity, but is still far from being pathogenically elucidated, as is the case with hypersensitivity.
Accordingly, pulpalgia has so far been treated with liners such as calcium hydroxide preparations, zinc oxide-eugenol cements, glass ionomer cements and carboxylate cements and others. These cements are designed to be mechanically coated on the surfaces of dentinal tubules to protect them against stimuli of external origin.
Problems with the calcium hydroxide preparations are that they are never hardened; they are incapable of forming roentgenograms; they are poor in strength and the like. The zinc oxide-eugenol cements consist of powders and liquid components which have to be mixed and kneaded together for use. Since the liquid/powder ratio should be about 0.5 and a large amount of the powder component should be incorporated into the liquid component, mixing and kneading above all involve much work. Moreover, this cement cannot be used for cases in which a composite resin is to be filled in place, because the liquid component or eugenol interferes with the polymerization of that resin. The zinc oxide-eugenol cements offer problems in strength, etc. as well.
The glass ionomer and carboxylate cements each consist of powders and liquid components which must be mixed and kneaded together for use. Mixing is again troublesome. Because of the liquid having pH of 1.2 to 1.7, the mixture causes a lingering pain to the patient upon filled. Since the cement film is likely to increase in thickness, there is a corresponding decrease in the thickness of a composite resin, offering an aesthetic problem, etc.
The handling problems with the therapies so far used to treat pulpalgia are that mixing and kneading is troublesome; the cement film is likely to increase in thickness and the like. From the patients' point of view, the problems are that they cause a lingering pain to the patients upon filled in place; no aesthetic color matching is achievable and the like.
Thus, clinicians have yet to find crucially efficacious therapy or an efficacious lenitives (or primers) for pulpalgia in spite of many people suffering from pulpalgia.
Various root canal fillers have been used with a view to blocking a passage from the oral cavity to around the root apex by closing up the formed and cleaned root canal and apical foramen, or promoting the growth and calcification of the connective tissue around the root apex. For instance, gutta-percha points, silver points, calcium hydroxide preparations, iodoform preparations, formaldehyde preparations and zinc oxide-eugenol type fillers have been used.